1. Field Of The Invention
The present invention relates to a washing machine for washing clothing or dishes, such as a clothing washer or a dish washer.
2. Description Of The Related Art
As an example of a washing machine of the type above-mentioned, there is known a dish washing and drying machine as disclosed in Japanese Patent Laid-Open Publication No. 60-48724(A)/1985. This dish washing and drying machine has a photosensor for detecting variations of the degree of light transmission in washing water inside of a water supply pipe disposed between a water reservoir at the bottom of a cleaning tank and a water inlet connected to a nozzle pump. The photosensor comprises a light emitting element and a light receiving element. With the use of the fact that the light receiving element changes in the amount of received light dependent on the degree of light transmission in water passing between the light emitting element and the light receiving element, the photosensor is adapted to detect variations of the degree of light transmission in washing water. According to the result of such detection, there is controlled the completion of the washing, rinsing, draining and drying steps.
However, commercially available light emitting elements are not constant in characteristics, so that they differ in light emitting output from one another. Likewise, commercially available light receiving elements are not constant in characteristics, so that the output voltages thereof vary with the amounts of received light.
This involves the likelihood that, even though different dishes which have been contaminated to the same extent, are washed with the use of the same drive circuit, the evaluation on the degree of light transmission in washing water varies with the combinations of light emitting/receiving elements. This may prevent the same washing effect from being produced.
In a system of controlling the steps according to the degree of light transmission as conventionally done, the degree of light transmission in washing water which is not contaminated, is generally measured to determine a reference value, and the degree of contamination of washing water is judged based on the difference between the reference value and an actually measured value. However, when a great amount of washing water which has been used at the previous washing, remains in the washing tank, water supplied into the washing tank becomes contaminated. If the degree of light transmission is measured to determine a reference value in such a situation, washing water which is actually dirty, might be erroneously judged as clean at the time of washing or rinsing, thus preventing a sufficient washing from being carried out.
In this connection, when the user manages to stop the operation to remove the washing water which has been used at the previous washing and which remains in the washing tank, and clean water is then supplied into the washing tank, the degree of light transmission can be accurately evaluated. However, this requires the user to remove the remaining water, thus lowering the maneuverability.